An electron beam discharge tube having a shaped collector with a plurality of cooling stages

ABSTRACT

In an electron beam discharge tube a fluid cooled electron collector has two cooling conduit systems each cooling a different part of the length of the collector, the interior surface having three main portions. Two portions are curved when viewed in section and extend over the length of the cooling stages. The third portion forms a conically tapered step between the first two portions, and extends over the region between the two cooling stages. The interior surface is shaped so that this third portion is subject to a lower intensity of electron bombardment than the average intensity elsewhere.

United States Patent Clan Noel OLoughlin; Graham Cyril Thomas Ball; Christopher John Edgcombe, all of Essex, England Inventors AN ELECTRON BEAM DISCHARGE TUBE HAVING A SHAPED COLLECTOR WITH A PLURALITY OF COOLING STAGES 9 Claims, 2 Drawing Figs.

US. Cl 313/30, s '313/2l,313/32,315/5.38 Int. Cl H0lj 1/42,

HOlj 23/02 Field of Search 313/21, 30,

[56] References Cited UNITED STATES PATENTS 3,140,421 7/1964 Spongberg 313 32 x 3,421,036 1/1969 Wolfram 315/538 X FOREIGN PATENTS 835,023 5/1960 Great Britain 15/538 Primary Examiner- Robert N egal Assistant Examiner-E. R. LaRoche Attorney-Baldwin, Wight, Diller & Brown ABSTRACT: In an electron beam discharge tube a fluid cooled electron collector has two cooling conduit systems each cooling a different part of the length of the collector, the interior surface having three main portions. Two portions are curved when viewed in section and extend over the length of the cooling stages. The third portion forms a conically tapered step between the first two portions, and extends over the region between the two cooling stages. The interior surface is shaped so that this third portion is subject to a lower intensity of electron bombardment than the average intensity e1- sewhere.

PATENTEUJUNISIS'II 3,585,429 'SHEETI UF 2 ATTORNEYS PATENTEUJUHISIQHO 3.585.429

SHEETZOUF 2 COLLECTOR OUTPUT c P CATCHER CAVITY B UNCHER CAVITY CATHODE \w I lNVENTORS cum NOEL omueuum, GRAHAM CYRH. THO-MRS BHLL ficHmswopHER JOHN EDGCDMBE BY a ATTORNEYS conduit systems each cooling a different part of the length of 0 the collector and each having its own coolant inlet. Tubes of this kind will hereinafter be termed, for the sake of brevity, tubes having fluid stage cooled collectors. The most important application of the invention is to Klystrons but it is applicable also to other forms of electron beam tubes with collectors, e.g. travelling wave tubes.

It is, of course, a well-known practice in high power electron beam tubes to provide fluid cooling for the collector, such fluid cooling being usually water and steam cooling. A common collector arrangement is one in which a-hollow collector, roughly projectile shaped and with an open end facing the electron gun of the tube, has its wall formed to provide longitudinal coolant conduits extending along almost the whole length of thecollector and arranged round it. The electron beam enters the open end of the collector and the electrons strike and are collected by the interior wall of the collector, of course, generating considerable heat. Water is admitted to the coolant conduits in parallel at their ends nearer the gun, is heated to steam in the conduits, and the steam is drawn off at the other ends of the conduits after which it is usually condensed and returned to a water coolant supply tank. Such an arrangement is, however, often insufficient to provide adequate cooling of the collector of a high power Klystron or the like unless the said collector is made uneconomically large and long, with uneconomically generous cooling conduit provision. A known way ofavoiding this difficulty is to provide a plurality of coolant conduit stages each cooling a different part of the length of the collector and each having its own water inlet. In a typical known arrangement of this nature the collector is provided with two sets of coolant conduitsit is possible though not usual to coolant more than two-the conduits of both sets being longitudinal and arranged round the collector with those ofone set extending over a first portion of the collector length and those of the other set extending over a second portion of that length. In normal practice each set extends over rather less than half the total length of the electrode. Water is admitted to the conduits of each set at their ends nearer the gun and steam drawn off from the other ends of the conduits of the two sets. Collectors thus fluid cooled in stages by sets of coolant conduits, extending over different successive parts of the length of the collector and each having its own coolant inlet, are what are herein termed fluid stage cooled collectors and the present invention relates to electron beam tubes having fluid stage cooled collectors.

A defect encountered with known electron beam tubes having fluid stage cooled collectors is that hot spots" (i.e. locally overheated areas) are apt to occur in the collector at regions between the coolant outlet end of one set of coolant conduits and the coolant inlet end of the next. It will be appreciated that, at the water inlet end of a set of conduits where the water has not yet been heated up to steam temperature, the rate of coolant flow is relatively low and the rate of cooling also relatively low. However the rate of heating of any particular part of the collector depends on the power input thereto due to electron bombardment thereof and if-as is the case with known fluid stage cooled collectorsthe intensity of the power input to the region in the neighborhood between the outlet end of one cooling stage and the inlet end of the next, is more or less the same as it is to other, better cooled, regions, local hot spots are liable to develop. The present invention seeks to avoid this defect.

According to this invention the interior wall of the collector of an electron beam tube having a fluid stage cooled hollow collector is so shaped that a portion of the interior surface of said wall in a region between one stage of cooling and the next is subjected to a substantially lower intensity of electron bombardment (when the tube is in use) than the average intensity of bombardment elsewhere on said interior wall.

Preferably the said interior wall is stepped at a region between one stage of cooling and the next to provide at the step a tapered interior surface, which is approximately tangential to or tapers away from the electron trajectories (when the tube is in use) to said region.

Preferably said interior wall is so shaped, over regions other than those between one stage of cooling and the next, as to receive (when the tube is in use) an approximately uniform value of power input per unit area by electron bombardment, said value being substantially higher than that of the power input by electron bombardment per unit area of regions between one stage of cooling and next.

In a preferred embodiment of the invention the collector is cooled in two stages and its interior surface comprises two portions, each so curved (as viewed in section) as to receive an approximately uniform value of power input by electron bombardment per unit area and each extending over approximately the length of a different stage of cooling, said two portions being joined to one another by an at least approximately conical portion with its smaller diameter at the end nearer the open end of the collector.

Preferably portions of the interior surface of the collector wall other than portions at regions between cooling stages are shaped so as approximately to satisfy the equation Wsin (0-B) Z17" sin 01/2 (where 2a is the cone angle of the electron beam entering the collector; W is the total beam power; 0 is the angle made by a given electron path to the collector interior wall with the axis ofthe collector axis; B is the angle between said wall and said axis at the point where said given path terminates at said wall and r is the length ofsaid given electron path from the apex of the electron beam to its end at the collector) and the angle between the axis of the collector and the interior surface of the collector at a region between cooling stages is not less than the angle 0. The invention is illustrated in the accompanying drawing FIG. 1 of which shows the interior shape of a preferred form of collector for a tube in accordance with the invention. FIG. 2 illustrates a collector, in accordance with the present invention, in an otherwise typical electron beam tube, e.g. a Klystron. Referring to FIG. 2 of the drawing, a high power Klystron provided with a customary cathode A and a buncher cavity B is shown. At the other end of the tube is a customary catcher cavity C and a shaped collector generally designated by the letter D.

Referring to FIG. 1 of the drawing, this shows an approximately projectile-shaped hollow collector which is cooled in two stages. The shaped hollow collector of the present invention may be used for the collector D forming part of the electron beam tube illustrated in FIG. 2. One stage of cooling is effected by a set of longitudinal conduits 1, equally spaced round the collector and formed in its wall. These conduits extend over somewhat less than half the length of the collector and have water inlets at their ends 2 nearer the open end 3 of the collector and steam outlets at their other ends 4. Steam drawoff pipes are shown at 5. The water inlet piping is not shown. The conduits I are, in the case illustrated, parallel to the collector axis.

The second stage of cooling is effected by a second set of longitudinal conduits 6 with water inlets at 7 and steam outlets at 8. So as not to complicate the figure the water and steam piping for the conduits 6 are not shown. The conduits 6 are also formed in the wall of the collector and are also equally spaced round it, but lie on the surface of an imaginary cone so as to conform more or less with the general shape of the collector.

The interior surface of the collector has three main portions of which two, 9 and 10, are curved as viewed in section, and the third 11, which is between them and joins them, is conical =a constant to form a conically tapered step between portions 9 and I0. The two portions 9 and 10 extend respectively approximately over the lengths of the two cooling stages and the portion 11 extends over the region between the two cooling stages. The portions 9 and 10 are shaped, over at any rate most of their surfaces, approximately to satisfy the equation (where 2a is the cone angle of the electron beam entering the collector; W is the total beam power; 0 is the angle made by a given electron path to the collector interior wall with the axis of the collector axis; and B is the angle between said wall and said axis at the point where said given path terminates at said wall and r is the length of said given electron path from the apex of the electron beam to its end at the collector).

The electron path of length r to the juncture of portions 9 and ll is shown by a broken line in the figure which also shows, by chain lines, the angles a, B and 0.

In the illustrated embodiment the taper ofthe portion ll is chosen to make B=0 so that the surface of this conical portion is tangential to the path shown. This is preferred as it leads to greatest economy in material. However a larger taper could be employed for the surface of portion 11, i.e. said surface could, if desired, taper away from the path shown. If the taper is less than that shown-which is permissible in some cases-power input to the portion 11 by electron bombardment will occur and will increase as the taper is reduced. Therefore the taper must not be so reduced that the heating of portion 11 is sufficient to produce hot spots in its region.

We claim:

1. An electron beam tube comprising an electron source, a fluid cooled hollow collector having an interior wall and at least two stages of cooling, an interior wall portion of said collector being tapered at a region between one of said at least two stages of cooling and the next, said interior wall portion being inclined away from the longitudinal axis of the tube in the direction of electron flow from said electron source, and the taper of said interior wall portion being such that electron bombardment of said interior wall portion is of substantially lower intensity than electron bombardment of other portions ofthe interior wall of said collector.

2. A tube as claimed in claim 1 wherein said interior wall is shaped, over regions other than those between one stage of cooling and the next, to receive an approximately uniform value of power input per unit area by electron bombardment, said value being substantially higher than that of the power input by electron bombardment per unit area of regions between one stage ofcooling and the next.

3. A tube as claimed in claim 1 wherein the collector is cooled in two stages and its interior surface comprises two portions, each so curved (as viewed in section) as to receive an approximately uniform value of power input by electron bombardment per unit area and each extending over approximately the length of a different stage of cooling said two portions being joined to one another by an at least approximately conical portion with its smaller diameter at the end nearer the open end of the collector.

4. A tube as claimed in claim 1 wherein the first said interior wall portion is approximately tangential to the electron trajectories to said region.

5. A tube as claimed in claim 4 wherein said interior wall is shaped, over regions other than those between one stage of cooling and the next, to receive an approximately uniform value of power input per unit area by electron bombardment, said value being substantially higher than that of the power input by electron bombardment per unit area of regions between one stage ofcooling and the next.

6. A tube as claimed in claim 1 wherein the first said interior wall portion tapers away from the electron trajectories to said region.

7. A tube as claimed in claim 3 wherein said interior wall is sha ed, over regions other than those between one sta e of coo mg and the next, to weave an approximately uni orm value of power input per unit area by electron bombardment, said value being substantially higher than that of the power input by electron bombardment per unit area of regions between one stage of cooling and the next.

8. A tube as claimed in claim 7 wherein the collector is cooled in two stages and its interior surface comprises two portions, each so curved (as viewed in section) as to receive an approximately uniform value of power input by electron bombardment per unit area and each extending over approximately the length ofa different stage of cooling, said two portions being joined to one another by an at least approximately conical portion with its smaller diameter at the end nearer the open end ofthe collector.

9. A tube as claimed in claim 8 wherein portions of the interior surface of the collector wall other than portions at regions between cooling stages are shaped so as approximately to satisfy the equation W sin (0-6) 47 sin 01/2 (where 201 is the cone angle of the electron beam entering the collector; W is the total beam power; 9 is the angle made by a given electron path to the collector interior wall with the axis of the collector axis; [3 is the angle between said wall and said axis at the point where said given path terminates at said wall and r is the length of said given electron path from the apex of the electron beam to its end at the collector) and the angle between the axis of the collector and the interior surface of the collector at a region between cooling stages is not less than the angle 6.

=a constant 

1. An electron beam tube comprising an electron source, a fluid cooled hollow collector having an interior wall and at least two stages of cooling, an interior wall portion of said collector being tapered at a region between one of said at least two stages of cooling and the next, said interior wall portion being inclined away from the longitudinal axis of the tube in the direction of electron flow from said electron source, and the taper of said interior wall portion being such that electron bombardment of said interior wall portion is of sUbstantially lower intensity than electron bombardment of other portions of the interior wall of said collector.
 2. A tube as claimed in claim 1 wherein said interior wall is shaped, over regions other than those between one stage of cooling and the next, to receive an approximately uniform value of power input per unit area by electron bombardment, said value being substantially higher than that of the power input by electron bombardment per unit area of regions between one stage of cooling and the next.
 3. A tube as claimed in claim 1 wherein the collector is cooled in two stages and its interior surface comprises two portions, each so curved (as viewed in section) as to receive an approximately uniform value of power input by electron bombardment per unit area and each extending over approximately the length of a different stage of cooling said two portions being joined to one another by an at least approximately conical portion with its smaller diameter at the end nearer the open end of the collector.
 4. A tube as claimed in claim 1 wherein the first said interior wall portion is approximately tangential to the electron trajectories to said region.
 5. A tube as claimed in claim 4 wherein said interior wall is shaped, over regions other than those between one stage of cooling and the next, to receive an approximately uniform value of power input per unit area by electron bombardment, said value being substantially higher than that of the power input by electron bombardment per unit area of regions between one stage of cooling and the next.
 6. A tube as claimed in claim 1 wherein the first said interior wall portion tapers away from the electron trajectories to said region.
 7. A tube as claimed in claim 3 wherein said interior wall is shaped, over regions other than those between one stage of cooling and the next, to receive an approximately uniform value of power input per unit area by electron bombardment, said value being substantially higher than that of the power input by electron bombardment per unit area of regions between one stage of cooling and the next.
 8. A tube as claimed in claim 7 wherein the collector is cooled in two stages and its interior surface comprises two portions, each so curved (as viewed in section) as to receive an approximately uniform value of power input by electron bombardment per unit area and each extending over approximately the length of a different stage of cooling, said two portions being joined to one another by an at least approximately conical portion with its smaller diameter at the end nearer the open end of the collector.
 9. A tube as claimed in claim 8 wherein portions of the interior surface of the collector wall other than portions at regions between cooling stages are shaped so as approximately to satisfy the equation (where 2 Alpha is the cone angle of the electron beam entering the collector; W is the total beam power; theta is the angle made by a given electron path to the collector interior wall with the axis of the collector axis; Beta is the angle between said wall and said axis at the point where said given path terminates at said wall and r is the length of said given electron path from the apex of the electron beam to its end at the collector) and the angle between the axis of the collector and the interior surface of the collector at a region between cooling stages is not less than the angle theta . 